Genetic Cross problems

In pigs, there are two loci which can influence skin color, genes A and B. Color ranges from roan (red) to sandy to white. Roan pigs have at least one dominant allele at both loci, sandy pigs have at least one dominant at either (but not both) loci, and white pigs have no dominant alleles.

a) Researchers mate a red pig (AABB) with a white pig. What genotype and phenotype ratios are expected in the progeny from this cross?

b) These progeny are then crossed to produce the next generation, which includes 48 little piglets. How many of each phenotype are expected if the genes assort independently?

c) Now assume that the two genes are so tightly linked that recombination does not occur in this cross. How many of each phenotype are expected?

Solution Preview

First, you need to understand the phenotypes that correspond to all the different genotypes.
Roan pigs: AaBb or AABB
sandy: Aabb, aaBb
white: aabb
a) red pig AABB x white pig aabb
The red pig can only contribute A for one gene and B for the other because all of the loci are dominant, while the white pig can only contribute ab to progeny because it has only recessive for all the loci.
Therefore, all of ...